Technical Field
Aspects of the present invention relate to Schottky barrier diodes and particularly relate to a Schottky barrier diode which oscillates or detects an electromagnetic wave in a frequency band within a frequency region from a millimeter-wave band to a terahertz band (equal to or higher than 30 GHz and equal to or lower than 30 THz) (hereinafter, called a terahertz-wave) and an apparatus using the same.
Description of the Related Art
A frequency region of terahertz-waves has an absorption peak derived from the structure and/or state of a biological material, pharmaceutical, electronic material, and many other organic molecules. Terahertz-waves are highly transmissive to materials such as paper, ceramics, resins, cloth. In recent years, imaging technologies and sensing technologies making use of such characteristics of terahertz-waves have been studied and developed. For example, their applications to safe fluoroscopic apparatuses alternative to X-ray apparatuses and in-line nondestructive inspection apparatuses in manufacturing processes are being expected.
Well known terahertz-wave detecting devices may include thermal detectors and quantum detectors. Examples of such a thermal detector may include a VOx microbolometer, TGS (Triglycine Sulphate) pyroelectric element, and a Golay cell using thermal expansion of gas. A thermal detector converts energy of an electromagnetic wave to heat and captures a change in heat electromotive force or resistance of a material due to a change in temperature to detect an electromagnetic wave. These devices may not necessarily be cooled but are slower to respond because of use of heat exchange. Examples of such a quantum detector may include an intrinsic semiconductor device (such as an MCT (HgCdTe) and a photoconductor) and a QWIP (Quantum Well Infrared Photodetector). A quantum detector captures an electromagnetic wave as a photon to detect a photovoltaic or resistance change in a semiconductor having a small band gap. Such a device is faster to respond but requires cooling because thermal energy at room temperature in the frequency region above is significant.
A terahertz-wave detecting device using a Schottky barrier diode has been developed which is faster to respond and does not require cooling. This detecting device captures an electromagnetic wave as a high frequency electric signal and rectifies with a diode the high frequency electric signal received through an antenna for detection. For example, Japanese Patent Laid-Open No. 09-162424 discloses a detecting device using a vertical Schottky barrier diode having two electrodes in a longitudinal direction on a substrate. The detecting device detects an approximately 28 THz electromagnetic wave (having a wavelength of 10.6 μm) from CO2 laser. Japanese Patent Laid-Open No. 60-18959 discloses a rectifier using a horizontal Schottky barrier diode having tow electrodes on a surface of a substrate. The rectifier includes a Schottky electrode having a guard ring at its edge to increase its reverse bias resistance. US Patent Application Publication No. 2007/0181909 discloses a Schottky barrier diode which detects a microwave and has a Schottky barrier having a silicon oxide at its edge to increase its reverse bias.
However, since a vertical Schottky barrier diode as disclosed in Japanese Patent Laid-Open No. 09-162424 uses its substrate as an earth electrode, limited types of antenna may be integrally formed. In such a horizontal device in the past as disclosed in Japanese Patent Laid-Open No. 60-18959, a semiconductor interface exposes to an element structure between two electrodes or in the vicinity of a diode on a semiconductor surface, larger leak current is generated by formation of a parasitic current path and/or larger noise may occur due to a state of the interface.
In a structure (FIG. 9) disclosed in US Patent Application Publication No. 2007/0181909, noise may occur due to lack of an interface between a semiconductor 901 and a silicon oxide 900. The disclosed device may detect microwaves at partial frequency bands, but its application to highly sensitive detection of terahertz-waves has been difficult.